JP5944903B2 - Interaction depth scintillation detector - Google Patents

Description

  [0001] This application claims the benefit of priority of US Provisional Patent Application No. 61 / 382,632 and US Provisional Patent Application No. 61 / 382,636, filed September 14, 2010. is there. The entire contents disclosed in these applications are hereby incorporated by reference into the present disclosure.

  [0002] The present invention relates to the field of imaging gamma-ray detectors, such as positron emission tomography (PET), and in particular, the transverse direction of gamma quantum interactions in the crystalline of the scintillator element of the detector. The present invention relates to a scintillation detector for detecting not only the coordinates but also the depth in an individual scintillator element (generally referred to as an interaction depth direction position (DOI)). This improves the spatial resolution of the PET (or any other) imaging system based on the ring detector position, especially at the viewing edge of the system.

  [0003] Positron emission tomography is a nuclear medicine three-dimensional imaging technique that generates a spatial (3D) map of the functional activity of living organisms, including human patients. This technique requires the introduction of a positron emitting nuclide attached to a biological material (eg, fluorodextrose) into the organism under investigation, which then penetrates the body and concentrates in the affected area After a predetermined time) based on examining its distribution within the organism under investigation.

  [0004] The positron emitted by the radionuclide moves several millimeters within the biological tissue of the organism under investigation before pairing with the electron. This pair annihilation event generates two 511 keV gamma quanta. These gamma quanta propagate from each other in almost opposite directions (180 ° ± 0.23 °). These two high energy photons can be captured to determine the approximate location of the pair annihilation event. In a typical PET system, these photons are absorbed by scintillation elements arranged in a ring around the organism under investigation, generating a burst of low energy visible photons that are then attached to each scintillation element. Detected by a photodetector. Each pair of high-energy photons moves in a substantially linear fashion (commonly referred to as a coincidence line (LOR)), so it is labeled by calculating the LOR intersection location (the so-called “sweet spot”). Can identify the location of the biological material High energy photons that have not arrived in pairs are eliminated by using simultaneous detection.

  [0005] In conventional systems, the spatial coordinates of a gamma photon absorption event can be determined only with the accuracy of the size of one scintillation element. Due to the high importance of the lateral coordinates, these scintillation elements have an elongated form with a relatively small cross-section facing the center of the field of view (see, for example, FIG. 1 showing the prior art). As a result, the spatial resolution at the center of the volume to be investigated becomes good, but the LOR for the absorption event becomes inaccurate, so that the spatial resolution gradually deteriorates toward one edge. Therefore, it is desirable to determine the position of the photon interaction along the long dimension of the scintillation element (this is usually referred to as the interaction depth direction position (DOI)). PET scanners that provide DOI measurements can more accurately assign LOR to photon absorption events, thus improving resolution non-uniformity across the field of view.

  [0006] Many methods have been proposed to improve DOI capability, but many of these methods rely on the addition of detector electronics, and are therefore quite complex hardware. Wear, and many other problems arise, such as gamma quantum absorption in forward facing electronics and increased dead space in the detector ring. Among these prior art methods, U.S. Patent Publication No. 2003/010597 by Zumer et al. Describes a dual detector readout technique in which two detectors are placed at opposite ends of a scintillation crystal bar. . A dual photodetector (PD) readout scintillation block cannot be packed as densely as a single PD readout block. For this reason, a dead space in which gamma quanta cannot be captured occurs between blocks. Moreover, this method requires twice as much PD and other electronic components (as compared to a single PD readout block), which increases manufacturing costs.

  [0007] In addition, phoswich detectors having two or more different scintillator layers distinguished by decay time are known for making DOI measurements. See, for example, Recontetti's US Pat. No. 4,843,245 using a multi-layer detector consisting of multiple scintillators with different decay times. This method allows for rough DOI indexing and improves the resolution of the PET imaging technique, but the resolution is limited by the discrimination performance of the detection electronics and by the choice of available scintillation materials. Moreover, it requires a much longer coincidence window, which makes the number of events collected more sparse and increases false coincidences, which makes image reconstruction more difficult.

  [0008] Another method disclosed in Sumiya et al., US Pat. No. 7,091,490, consists of the use of a multi-layer scintillator detector that incorporates both light sharing (distribution) and decay time discrimination. This configuration requires multiple scintillation crystals that are subjected to various surface treatments and separated by various optical interfaces (incorporated into the detector elements) that are transparent, reflective or opaque. This makes the method even more complex than the method using a dual detector, which is probably correct. This is because the composition of the scintillation element becomes very complicated.

  [0009] One particular method uses light sharing along the long dimension between two adjacent scintillation crystals. This does not lead to complication of the detector electronic device, and the DOI information can be extracted based on the ratio of the optical signals collected by the detectors attached to each crystal in pairs. This is the gist of Rewellen et al., US Pat. No. 7,956,331, with a shaped opaque screen and / or spatial light interface layer between adjacent crystals and a solid-state micropixel detector. It provides a means of adding DOI functionality to a PET detector without introducing any additional electronic devices.

US Patent Publication No. 2003/010597 U.S. Pat. No. 4,843,245 US Pat. No. 7,091,490 US Patent No. 7,956,331

  [0010] The method described above meets the technical requirements for a PET system with a DOI function. However, many problems associated with detector manufacture remain unresolved. For example, as with all conventional PET detectors, the method outlined in Rewellen et al., US Pat. No. 7,956,331, can be used to assemble each scintillation crystal pair from individual elements to share light. It is necessary to place an opaque layer and a transparent layer between these elements. Next, each of the pair of crystals must be assembled (approximately manually) into a detector block with an appropriate reflective and light blocking layer disposed between the pair of crystals. However, it is desirable to manufacture the scintillation detector block in a more industrial and automated manner while retaining important DOI functions. The present invention provides, among other things, another method for adding DOI functionality to a PET scintillation detector in a cost-effective manner that opens up the possibility of further automation and improvement of PET detector manufacturing. .

  [0011] The present invention relates to a scintillation detector that can detect the position or depth of a gamma photon interaction that occurs in a scintillator. One embodiment of the present invention includes at least a pair of bonded scintillation crystal bars, each pair of bonded scintillation crystal bars being positioned in a side-to-side configuration, and on each long side. It contains two individual scintillation crystal bars connected along. These scintillation crystal bars are optically isolated from each other and from the surrounding environment on the four long sides. The remaining two small faces of each of the crystal bars act as light windows and their surfaces are polished and coated as necessary to facilitate or limit light coupling to the exterior of the crystal bar. Is given. Two adjacent connecting windows of each pair of crystal bars are optically connected to each other by a reflective element (or “rooftop”) attached to these crystal bars by an optical interface layer. One embodiment further includes a retroreflective prism having a coated reflective surface for sharing light between one scintillation crystal bar and the other scintillation crystal bar.

  [0012] The scintillation detector further includes a solid state semiconductor photodetector optically coupled to an adjacent light window of each pair of coupled scintillation crystal bars opposite the light window coupled to the reflective element. Including. The solid-state photodetector includes an array of separate photosensitive areas, each of which has a one-to-one relationship with each of the photosensitive areas in the open light window of each scintillation crystal bar of each bond pair. So that they are optically coupled to each other, preferably on a flat surface of a common substrate.

  [0013] A burst of visible photons (generated as a result of a gamma photon interaction event) within one of the bars of a binding pair of scintillation crystal bars is shared between the two associated crystal bars. The information about the location of this event along the length of the attached scintillation crystal bar is then used to determine the ratio of the optical signal recorded by the respective photosensitive area of the photodetector connected to each light output window of the coupling bar. It may be determined by calculating.

  [0014] These and other embodiments of the invention are described in further detail in the following detailed description and accompanying drawings. However, it should be understood that various modifications, changes and substitutions may be made to the specific embodiments disclosed herein without departing from their essential spirit and scope. It is. Moreover, all of the various documents cited herein are expressly incorporated by reference into the disclosure of this document in their entirety for all purposes.

  [0015] These examples supplement the above general description and the following detailed description to better understand the present invention. Moreover, like reference numerals have been used throughout several drawings to indicate similar features.

[0016] FIG. 1 a (prior art) is a schematic side view of a conventional PET detector ring 1 having a field boundary 2, which shows an electron positron pair annihilation event 3 occurring toward one edge of the field of view as a true LOR 4. And an erroneous (misaligned) LOR5 measured from the co-measured gamma photons captured by the corresponding detector elements. [0017] FIG. 1b (prior art) is a solid state photodetector in which the base portion 6 is coupled to an output window 7 of a scintillation crystal bar 8 separated by an optical interface layer 9 and an optical separation layer 10. 1 is a schematic perspective view of a technical PET detector (Rewelen et al. US Pat. No. 7,956,331). [0018] FIG. 2a is a cross-sectional view of a first embodiment of the novel detector, with its base portion 6 on its common substrate connected to the output window 7 of the combined scintillation crystal bar 8, its corresponding photosensitive area. This corresponds to a photodetector having These crystal bars 8 have light guide chamfered surfaces 11 (these chamfered surfaces form a roof 16) and are connected to each other by an optical interface layer 12 and a distal connection window 13. Adjacent surfaces of these crystal bars 8 are attached to each other via a light separation layer 14, and the outside thereof is covered with a light blocking coating 15. [0019] FIG. 2b is a cross-sectional view of a second embodiment of the novel detector, in addition to elements similar to those in FIG. 2a (denoted by the same reference numerals), between the coupled scintillation crystal bars 8. Fig. 6 shows a roof 16 formed of retroreflective crystal elements configured to share light. The rooftop 16 is connected to the crystal bar 8 via the optical interface layer 17 and the distal connection window 18. [0020] FIG. 2c is a cross-sectional view of another embodiment of the novel detector, in addition to elements similar to those of FIG. 2a (with the same reference numbers), U-shaped scintillation crystals 19 is shown together with two proximal connecting windows 7, a light guide chamfered surface 11 (these chamfered surfaces form the rooftop 16), and a narrow opening provided by the light separating layer 14. [0021] FIG. 3a illustrates a method in which light emitted by gamma photon interaction is guided by a chamfer that forms part of the present invention. Reference numeral 20 denotes a γ photon interaction place (where visible light is generated), and an arrow 21 indicates most of the emitted light shared with the second scintillation crystal bar. [0022] FIG. 3b (prior art) shows that in a conventional light sharing method, a large amount of light 22 is reflected back to the detector sensing area connected to the crystal bar where the gamma photon interaction occurs (see dashed line). FIG. [0023] FIG. 4a shows the angle 23 and the size 24 of the light guide chamfer position. [0024] FIG. 4b shows the light guide chamfered face size 24, the crystal bar width 25, and the connecting window size 26, along with the coupling window and light guide chamfering position, for light sharing between the two photodetectors. It is a figure shown as a parameter which can be used in adjusting a characteristic and quantity. [0025] FIG. 5a is a perspective view of a detector block according to another embodiment of the present invention, the detector block comprising a pair of chamfered crystalline scintillation bars 8 (FIGS. 2a, 3a, 4a). Each having a chamfered pair of crystalline chamfers in the form of a detector) and connected to a 2n × k array of photodetectors 6. [0026] FIG. 5b is a perspective view of a detector block according to another embodiment of the present invention, the detector block comprising a pair of crystalline scintillation bars 8 (of a crystalline pair in the form of a detector shown in FIG. 2b). Each with a pair of crystal bars connected to each other via a distal connection window and a retroreflector 16, and 2 n × of the photodetector 6 via a proximal output window. connected to an array of k.

  [0027] The present invention relates to a scintillation detector, which can detect the depth coordinate of a gamma photon interaction that occurs in the scintillation material of the detector, thereby improving the resolution of a ring-like PET imaging system. To do. In one embodiment, referring to the accompanying drawings (particularly FIG. 2a), the present invention relates to a scintillation detector for measuring the depth position of a gamma photon interaction, comprising at least a pair of coupled scintillation crystal elements or bars 8. . Each pair of coupled scintillation crystal bars 8 includes (i) a light separation layer 14 positioned between two separate scintillation crystal bars 8 to limit light sharing between the scintillation bars 8, and (ii) A distal connecting window 13 provided at the distal end of each of the combined scintillation crystal bars (upper part of all figures except FIG. 1a), in optical contact with each other, possibly with light A distal coupling window 13 in optical contact with the interface layer 12 in between, and (iii) a light guide chamfered surface 11 (known in the art) provided at the distal end of each of the coupled scintillation crystal bars 8 Different from the rectangular crystal bar shape). The light guide chamfered surface 11 may have various sizes 24 with respect to the width of each crystal bar 8, and make various cut angles 23 with respect to the longest face of each crystal bar 8 (while May be required to optimize the sharing of light among a plurality of coupled crystal bars 8 in which γ photon interactions occur). Similarly, the distal connection window 13 may be provided with various sizes 26 and shapes to further optimize light sharing (see FIGS. 4a and 4b). Unlike the conventional light sharing method (refer to FIG. 3 b showing the prior art), the light guide chamfered surface 11 allows a small part of the light generated by the γ photon interaction event to be transferred to each pair of coupled scintillation crystal elements 8. Reflects to reach the other crystal bar. In the prior art shown in FIG. 3b, this part of the generated light is reflected back into the same crystal bar.

  [0028] In order to collect more visible light generated by gamma photon interaction events and optimize light sharing between two separate scintillation bars 8, the surface of each bar 8 is mechanically treated ( For example, grinding or polishing may be performed, and chemical treatment (for example, etching) may be performed. The proximal output window 7 is preferably polished so that sufficient light collection is possible and light transmission is enhanced. In order to further improve light collection and prevent crosstalk between one pair of coupled scintillation crystal bars 8 and another pair of coupled scintillation crystal bars 8, the outer surface of each scintillation crystal bar 8 is provided with a light absorbing cover or light. It may be covered with a reflective cover. Further, the light blocking layer 14 may be non-uniform in opacity, may be reflective, and / or act as a light diffusing plate.

[0029] Materials of the individual scintillation crystal bar 8 preferably, LFS, SLO, LYSO, GSO , LGSO, LuAP, BGO, is selected from the group consisting of NaI and PbWO _4. The individual bars of each coupled scintillation crystal bar pair comprising the detector are preferably formed of the same scintillation material. This material is preferably LFS scintillation crystals (available from Zecotec Photonics). The material of each scintillation crystal bar 8 is preferably NaI: TI with a light output higher than 80%, a fluorescence decay time of less than 50 ns, and a density greater than 6 g / cm ³ .

[0030] In another embodiment, the scintillation detector of the present invention further includes optically connecting the photosensitive region of the detector to the proximal output window 7 of each of the individual scintillation crystal bars 8 in a one-to-one relationship. A solid state semiconductor photodetector 6 (available from Zecotec Photonics). Unlike conventional position sensitive photomultiplier tubes (PMTs) known in the art, the solid state semiconductor photodetector 6 of the present invention is a discrete substrate disposed on a common substrate that forms a generally flat surface. Including an array of sensing regions. Each sensing region of the photodetector includes an array of micropixel avalanche photodiodes, which are preferably embedded in the material of each sensing region. The pixel (independent pn junction) density of each sensing region is preferably greater than 1000 pixels / mm ² . A pixel density of 5000 pixels / mm ^{2 to} 15000 pixels / mm ² is sufficient for many applications, but more preferably about 40000 pixels / mm ² or more. As shown in the accompanying drawings, the proximal output window 7 of each scintillation crystal bar 8 is connected in a one-to-one relationship to each of the respective sensing areas of the photodetector 6. An overall perspective view of this embodiment of the invention is shown in FIG. 5a. In this figure, an array of n × k pairs of crystal scintillation bars 8 is connected in a one-to-one relationship with each of the scintillation crystal bars 8 to a solid-state photodetector 6 having 2n × k distinct sensing areas. Has been.

  [0031] In another embodiment, referring to FIG. 2b, the present invention is similar to that described above, but instead of forming a light guide chamfer at the distal end of each scintillation crystal bar. Each scintillation detector has a distal light coupling window 18 with each crystal bar of each coupled pair of crystal bars coupled to a retroreflector 16 (ie, a rooftop or rooftop element). The retroreflector 16 preferably has a prism shape and is formed of a material whose refractive index is the same as or similar to that of the scintillation crystal bar 8. The angle and size of the light guide surface of the retroreflector is similar to the size and angle of the light guide chamfer surface of the first embodiment shown in FIGS. 4a and 4b. Changes may be made as necessary to optimize the sharing of light between each. The surface of the retroreflector is preferably optically polished to facilitate internal light reflection and may be covered with a reflective coating depending on the particular configuration of the scintillation detector ( Instead of connecting sides preferably attached to the distal connecting window of each pair of bonded scintillation crystals 8, an optical adhesive, or (preferably having the same or at least similar refractive index as the material of the scintillation crystal bar) Use another optical interface layer). The connecting surface of the retroreflector 16 and the distal connecting window of the crystal bar 8 may be provided with an anti-reflective coating to improve the optical coupling between the crystal bars. In addition, the entire retroreflector attached to each coupled pair of scintillation crystal bars 8 can be single-ended in a single operation by stamping, injection molding, or another similar technique using optically clear plastic. May be manufactured as units (but units that are optically isolated from each other). After manufacture, the retroreflector is attached to the distal end of an array of bonded scintillation crystal bars, as shown in FIG. 5b. This embodiment has all the advantages of the above-described embodiments, yet is easier to manufacture and can use cheaper materials. The whole of this embodiment of the invention is shown in the perspective view of FIG. Here, the proximal end of an array of nxk pairs of scintillation bars 8 is in a one-to-one correspondence with each of the scintillation crystal bars 8 to a solid-state photodetector 6 having 2 nxk distinct sensing areas. Connected in a relationship. Each coupled pair of scintillation crystal bars that make up the array is connected at its distal end to a corresponding retroreflector 16. An array of retroreflectors can be manufactured as a single assembly part and attached in a single simple operation.

  [0032] In yet another embodiment of the present invention, referring to FIG. 2c, one U-shaped scintillation crystal 19 is provided in place of each bond pair of the scintillation crystal bar of the above-described embodiment. The branch portions (divided portions) of the U-shaped scintillation crystal 19 have the proportions (proportions) of the crystal bar 8 of the other examples shown in FIGS. 2a, 2b, 3a, 4a, 5a and 5b. It is similar to that. Between these branches, a narrow slot is formed by being narrowed by a light separation layer 14 similar to the similar layer of the other embodiments. At the distal end of the U-shaped scintillation crystal bar 19, a light guide chamfered surface 11 (which forms a rooftop) similar to that in other embodiments of the present invention using a pair of separate scintillation crystals 8. Is provided. This configuration has the advantage of eliminating the optical interface that exists between the crystal bars of each bonded pair of scintillation crystals of other embodiments of the invention. This eliminates the loss due to Fresnel reflection and the optical loss due to internal reflection, and improves the light collection efficiency.

  [0033] All possible embodiments of the present invention, including the embodiments described above, have significant advantages over dual detector readout techniques (using a photodetector at each end of the scintillation crystal bar). Given the same geometric dimensions and the same lateral spatial resolution, the novel detector device of the present invention provides twice the optical path between detectors compared to the dual detector technology. provide. This increases the output signal ratio. This improvement is expected to improve the accuracy of DOI measurement.

  [0034] The invention is not limited to the specific details disclosed. Although the invention has been described with reference to the embodiments shown and described herein, the invention may be practiced in other specific ways or configurations without departing from the spirit and essential characteristics of the invention. May be. Accordingly, the embodiments described above are to be considered in all respects only as illustrative and not restrictive. Therefore, the scope of the present invention is shown not by the above description but by the appended claims, and all modifications within the meaning and scope equivalent to the claims are to be included in the scope. .

6 ... Photodetector 7 ... Proximal output window 8 ... Coupling scintillation crystal bar 11 ... Light guide chamfered surface 12 ... Optical interface layer 13 ... Distal connection window 14 ... Light separation layer (light blocking layer)
DESCRIPTION OF SYMBOLS 15 ... Light shielding coating 16 ... Retroreflector 17 ... Optical interface layer 18 ... Distal light connection window 19 ... Scintillation crystal 22 ... Light 23 ... Cut angle 24, 26 ... Size

Claims (15)

A scintillation detector for detecting the position of the gamma photon interaction,
An array of two or more elongated first and second scintillation crystal elements coupled together along their respective long sides;
Comprising an array of separate photosensitive areas disposed on a common substrate of solid state semiconductor photodetectors;
The array of first and second scintillation crystal elements comprises a proximal output window optically coupled in a one-to-one relationship to the array of distinct photosensitive regions;
The first and second scintillation crystal elements comprise a rooftop at a distal end of the elements;
The rooftop is
Optically connecting one of the first and second scintillation crystal elements to the other;
Configured to reflect and transmit light generated by the gamma photon interaction from one of the first and second scintillation crystal elements to the other ;
The roof is formed by first and second light guide chamfered surfaces,
The first light guide chamfered surface is an integral part of the first scintillation crystal element;
The scintillation detector, wherein the second light guide chamfered surface is an integral part of the second scintillation crystal element . A scintillation detector according to claim 1,
The first and second scintillation crystal elements of the array of first and second scintillation crystal elements form a plurality of coupled scintillation crystal pairs;
Each of the coupled scintillation crystal pairs is optically blocked from each of the other coupled scintillation crystal pairs. A scintillation detector. A scintillation detector according to claim 2,
Each of the coupled scintillation crystal pairs comprises a light separation layer positioned between the first and second scintillation elements;
The light separation layer limits light sharing between the first and second scintillation elements. A scintillation detector. A scintillation detector according to claim 1 ,
The distal ends of the first and second scintillation crystals comprise opposing optical coupling windows;
The light coupling window is positioned between the first and second light guide chamfered surfaces and is separated from each other by having a light coupling layer disposed therebetween. A scintillation detector according to claim 3,
The roof is formed by a separate prism element,
The separate prism element is formed of a material having the same or substantially the same refractive index as that of the first and second scintillation elements. A scintillation detector. A scintillation detector according to claim 5 ,
Each of the first and second scintillation elements comprises a distal light coupling window;
The separate prism element is optically coupled to the distal light coupling window with a light coupling layer disposed therebetween, a scintillation detector. A scintillation detector according to claim 1,
The first and second scintillation crystal elements are:
Formed integrally with each other,
A scintillation detector forming first and second branches of a single U-shaped scintillation crystal element. A scintillation detector according to claim 7 ,
The first and second branches are separated from each other by interposing an optical coupling layer therebetween. A scintillation detector. A scintillation detector according to claim 3,
The light separating layer has a non-uniform opacity scintillation detector. A scintillation detector according to claim 3,
The light separation layer is a scintillation detector having reflectivity or diffuse reflectivity. A scintillation detector according to claim 1,
The rooftop forms an angle of about 35 ° to about 80 ° with respect to the long side surfaces of the first and second scintillation crystals. A scintillation detector according to claim 2,
Each of the pair of scintillation crystals has a light blocking layer on its outer surface. A scintillation detector. A scintillation detector according to claim 12 ,
The light blocking layer is a scintillation detector having reflectivity or diffuse reflectivity. A scintillation detector according to claim 1,
The scintillation detector, wherein the first and second scintillation crystal elements are substantially the same as each other and are selected from the group consisting of crystals of LFS, SLO, LYSO, GSO, LGSO, LuAP, BGO, NaI, and PbWO4. A scintillation detector according to claim 1,
The array of distinct photosensitive areas forms an array of distinct micropixel avalanche photodiodes. Scintillation detector.

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